1. Field of the Invention
The present invention relates to a lighting system in which controllable lights and controllable emergency current lights are connected, respectively, to a first current supply and to an emergency current supply, the lights being controlled by associated control devices. 2. Description of the Related Art
For the illumination of extensive premises or buildings there are often employed lighting systems having a plurality of de-centrally installed lights, the lights being controlled by a central control device which controls at least the switching on and switching off, possibly also the dimming, of the individual lights. For safety reasons as a rule there is provided with such lighting systems also an emergency current or emergency lighting operation, in which a few of the lights, or even special emergency lights, are operated at a power which may be reduced.
A lighting system described in DE 27 47 173 A1 contains for example autonomous emergency current supply devices which have their own emergency lamps. The emergency current supply devices contain an emergency current battery and a charging device connected with the mains. In the case of mains failure, the emergency current light is then switched on by means of a switch. A further lighting system having emergency current operation is described in EP 0 490 329 B1. Here, fluorescent lamps are connected with the mains via electronic ballasts. If mains supply is disrupted or fails there is applied to the supply lines for the ballasts a battery d.c. voltage of the level of the mains voltage. The switch-over from the a.c. voltage of the normal mains to the d.c. voltage is automatically recognized by the ballasts. These then continue to generate an a.c. voltage for the operation of the fluorescent lamps but control the lamps in a predetermined emergency lighting mode, in which for example only a few particular lamps are operated at circa 50% of the maximum lamp power.
With the lighting system of EP 0 490 329 B1 just described, the same supply voltage is delivered to all lights, whereby each ballast individually checks for itself whether it is the normal mains voltage or not, and then switches into the emergency lighting mode if a mains disruption is recognized. For reasons of safety, a lighting system is, however, often so configured that only a certain proportion of the lights are provided for emergency current illumination, these lights being connected not to the general current supply but to an emergency current supply separate or independent thereof. This emergency current supply is an additional a.c. voltage supply, preferably independent of the normal current supply, which in the case of a total failure of the mains can be replaced by a d.c. voltage source. In this case, however, the process described in EP 0 490 329 B1 cannot be used, since in accordance with the features just described, the emergency current lights are supplied independently of the normal lights with current so that they or their ballasts or control devices are not in a position to monitor the normal mains voltage for the normal lights. A disruption of the current supply for the normal lights is thus not immediately recognizable for the emergency lights.
In order, despite this, to inform the emergency current lights of a failure or disruption of the normal current supply it has previously been usual to monitor the mains for the normal lights of the lighting system for disruption with a special monitoring device, and upon determination of a fault to temporarily interrupt the emergency current supply. This interruption is maintained for a certain time, so that it is also in effect recognized or interpreted as a control command for the activation of the emergency light operation by the control devices of the emergency current lights. Such a temporary interruption of the emergency current supply is, however, disadvantageous since there is necessary therefor a not inconsiderable technical outlay. If the emergency current lights are gas discharge lamps then further the possibility cannot be excluded that these may first have to be newly preheated or newly started, as a result of which a loss of time until the activation of the emergency lighting must be accepted.